The invention is a process for removing bacterial endotoxin from Gram-negative polysaccharides without incurring substantial loss of polysaccharide.
Bacterial endotoxin is a potent pyrogen that can often produce fever reactions when administered to patients. Endotoxin is an integral component of the outer cell surface of Gram-negative bacteria. It exists in its natural state as a complex of lipid, carbohydrate and protein. When highly purified, endotoxin does not contain protein, and by its chemical composition is referred to as a lipopolysaccharide (see Weary and Pearson, Bio. Pharm. April (1988) pp. 22-29).
The outer-wall layer of Gram-negative bacteria serves as an outer barrier through which materials must penetrate if they are to reach the cell. It is selectively permeable. Generally, endotoxin is released in large amounts only when the cell wall is lysed.
Removal of contaminating endotoxin from Gram-negative polysaccharides is important when the polysaccharide is to be administered to humans. Endotoxins in large quantities can cause shock, severe diarrhea, fever and leukopenia followed by leukocytosis, and can elicit the Shwartzman and Sanarelli-Shwartzman and phenomena.
U.S. Pat. No. 4,695,624, issued to Marburg et al., describes covalently-modified polyanionic bacterial polysaccharides, stable covalent conjugates of these polysaccharides with immunogenic proteins, and methods of preparing the polysaccharides and conjugates and of confirming covalency. The patent describes purification of the polysaccharide in Example 1, beginning in column 14. After fermentation, inactivation and cell removal, the resulting product undergoes a series of cold ethanol fractionations. Following phenol extraction are diafiltration, ethanol precipitation, ultracentrifugation in ethanol, and collection of the finished product.
Frequently, the amount of contaminating endotoxin remaining after the above-described procedure is higher then desired.
Methods for removing endotoxin which are known in the art are described by Weary and Pearson (ibid): rinsing with nonpyrogenic solution (Feldstine et al., J. Parenter. Drug Assoc., 33, p. 125 (1979) and Berman et al., J. Parenter. Sci. Technol., 41, p. 158 (1987); distillation; ultrafiltration using membranes rated by molecular weight exclusion (Sweadner et al., Appl. Environ. Microbiol., 34, p. 382 (1977) and Henderson et al., Kidney Int., 14, p. 522 (1978); reverse osmosis using thin cellulose acetate or polyamide materials (Nelson, Pharm. Technol., 2, p. 46 (1978); electrostatic attraction (Gerba et al., Pharm Technol., 4, p. 83 (1980) and Hou et al., Appl. Environ. Microbiol., 40, p. 892 (1980); hydrophobic attraction using aliphatic polymers (Robinson et al., in Depyrogenation (Parenteral Drug Association, Philadelphia (1985), pp. 54-69); adsorption using activated carbon (Berger et al., Adv. Chem. Ser., 16, p. 169 (1956), Gemmell et al., Pharm J., 154, p. 126 (1945), and Brindle et al., Pharm. J., 157, p. 85 (1946); and affinity chromatography (Soter, Bio/Technology, 12, p. 1035 (1984).
Sawada et al., Applied and Environmental Microbiology, April 1986, pp. 813-820, describe removal of endotoxin from water by microfiltration through a microporous polyethylene hollow-fiber membrane. Gerba et al., Applied and Environmental Microbiology, December 1985, pp. 1375-1377, describe endotoxin removal from various solutions using charged nylon and cellulose-diatomaceous earth filters. Nolan et al., Proceeding of the Society for Experimental Biology and Medicine, vol. 149, pp. 766-770 (1975), describe endotoxin binding by charged and uncharged resins.
Sweadner, K. et al., Applied and Environmental Microbiology, Vol. 34, pp. 382-385 (1977) explain that lipopolysaccharide often exist in an aggregated state, and that dissociating the lipopolysaccharide with detergent or chelating agents can facilitate its removal from aqueous solutions by filtration. Shands, J. et al., J. Biological Chemistry, Vol. 255, pp. 1221-1226 (1980), show that lipopolysaccharide is associated with divalent cations, and that dispersion of Gram-negative lipopolysaccharides can be achieved using deoxycholate.
McIntire, et al, Biochemistry, Vol. 8, No. 10, pp. 4063-4066 (1969) describes reversible inactivation, by sodium deoxycholate, of Escherichia coli lipopolysaccharide. Ribi, et al., Journal of Bacteriology, Vol. 92, No. 5, pp. 1493-1509 (1966) described physical and biological properties of endotoxin treated with sodium deoxycholate.
It is a purpose of the present invention to provide an effective method of obtaining Gram-negative polysaccharide mixtures having low or negligable levels of endotoxin, without suffering substantial loss of polysaccharide.
It is also a purpose of the present invention to provide a process for eliminating endotoxin from a solution of bacterial polysaccharide while minimizing the removal of bacterial polysaccharides and other desired species.